The Memories of NK Cells: Innate-Adaptive Immune Intrinsic Crosstalk

Implications of vaccine non-specific effects on licensure of new vaccines

Immune memory was for a long time thought to be an exclusive feature of the adaptive immune system. Emerging evidence has shown that the innate immune system may exhibit memory which has been termed as trained immunity or innate immune memory. Trained immunity following vaccination may produce non-specific effects leading to reduction in morbidity and mortality from heterologous pathogens. This review looked at trained immunity as a mechanism for vaccine induced non-specific effects, mechanisms underlying trained immunity and known vaccine non-specific effects. A discussion is also made on the implications these vaccine non-specific effects may have on overall risk-benefit ratio evaluation by National Medicines Regulatory Authorities (NMRAs) during licensure of new vaccines. Epigenetic remodeling and "rewiring" of cellular metabolism in the innate immune cells especially monocytes, macrophages, and Natural Killer (NK) cells have been suggested to be the mechanisms underlying trained immunity. Trained immunity in other innate cells has largely remained elusive up to date. Non-specific effects have been extensively documented with Bacille Calmette-Guerin (BCG), measles vaccine and oral polio vaccine but it remains unclear if other vaccines may exhibit similar effects. All known vaccine non-specific effects have come from observations in epidemiological studies conducted post-vaccine licensure and roll out in target populations. It remains to be seen if early identification of non-specific effects especially those with protective benefits during the clinical development of new vaccines may contribute to the overall risk-benefit ratio evaluation during licensure by NMRAs.

Breast cancer immunotherapy: a comprehensive review

Cancer remains a major health problem despite numerous new medical interventions that have been introduced in recent years. One of the major choices for cancer therapy is so-called adoptive cell therapy (ACT). ACT can be performed using both innate immune cells, including dendritic cells (DCs), natural killer (NK) cells, and γδ T cells and acquired immune T cells. It has become possible to utilize these cells in both their native and modified states in clinical studies. Because of considerable success in cancer treatment, ACT now plays a role in advanced therapy protocols. Genetic engineering of autologous and allogeneic immune cells (T lymphocytes, NK cells, macrophages, etc.) with chimeric antigen receptors (CAR) is a powerful new tool to target specific antigens on cancer cells. The Food and Drug Administration (FDA) in the US has approved certain CAR-T cells for hematologic malignancies and it is hoped that their use can be extended to incorporate a variety of cells, in particular NK cells. However, the ACT method has some limitations, such as the risk of rejection in allogeneic engrafts. Accordingly, numerous efforts are being made to eliminate or minimize this and other complications. In the present review, we have developed a guide to breast cancer (BC) therapy from conventional therapy, through to cell-based approaches, in particular novel technologies including CAR with emphasis on NK cells as a new and safer candidate in this field as well as the more recent aptamer technology, which can play a major role in BC immunotherapy.

Role of natural killer and B cell interaction in inducing pathogen specific immune responses

The innate lymphoid cell (ILC) system comprising of the circulating and tissue-resident cells is known to clear infectious pathogens, establish immune homeostasis as well as confer antitumor immunity. Human natural killer cells (hNKs) and other ILCs carry out mopping of the infectious pathogens and perform cytolytic activity regulated by the non-adaptive immune system. The NK cells generate immunological memory and rapid recall response tightly regulated by the adaptive immunity. The interaction of NK and B cell, and its role to induce the pathogen specific immunity is not fully understood. Hence, present article sheds light on the interaction between NK and B cells and resulting immune responses in the infectious diseases. The immune responses elicited by the NK-B cell interaction is of particular importance for developing therapeutic vaccines against the infectious pathogens. Further, experimental evidences suggest the immune-response driven by NK cell population elicits the host-specific antibodies and memory B cells. Also, recently developed humanized immune system (HIS) mice and their importance in to understanding the NK-B cell interaction and resulting pathogen specific immunity has been discussed.

The phenotype of CD3-CD56bright and CD3-CD56dim natural killer cells in systemic lupus erythematosus patients and its relation to disease activity

Introduction

Systemic lupus erythematosus (SLE) patients have decreased natural killer (NK) cell counts. The decrease in the number of NK cells has implications for a decrease in the function of NK cells which can affect the progression of SLE disease. The study aim was to determine profiles of CD3-CD56^bright and CD3-CD56^dim NK cells in SLE patients and their relation to disease activity.

Material and methods

This study included 36 patients of SLE who fulfilled the ACR 1997/SLICC 2012 criteria, women aged 18-49 years. Disease activity was assessed by the Mex-SLEDAI. Peripheral blood samples from SLE patients were analyzed by flow cytometry to evaluate NK cell subsets, according to differential expression of the main subset of NK cells, which is CD3-CD56^bright and CD3-CD56^dim.

Results

The mean percentage of regulatory NK cell count (CD3-CD56^bright) in active SLE patients was significantly lower (p = 0.000) than in inactive SLE patients. The mean percentage of cytotoxic NK cell count (CD3-CD56^dim) in active SLE patients was significantly (p = 0.000) higher than in inactive SLE patients. A correlation was observed between two subsets of NK cells with disease activity (p = 0.00). The percentage of CD3-CD56^bright NK cells was negatively correlated with disease activity (r = -0.766), whereas the percentage of CD3-CD56^dim NK cells positively correlated with disease activity (r = 0.761).

Conclusions

There is a difference in the mean percentage of the number of NK cells (CD3-CD56+) in both a subset of regulatory NK cells (CD3-CD56^bright) and cytotoxic NK cells (CD3-CD56^dim) in active and inactive SLE patients and it is closely related to SLE disease activity.

Pathological and protective roles of dendritic cells in Mycobacterium tuberculosis infection: Interaction between host immune responses and pathogen evasion

Dendritic cells (DCs) are principal defense components that play multifactorial roles in translating innate immune responses to adaptive immunity in Mycobacterium tuberculosis (Mtb) infections. The heterogeneous nature of DC subsets follows their altered functions by interacting with other immune cells, Mtb, and its products, enhancing host defense mechanisms or facilitating pathogen evasion. Thus, a better understanding of the immune responses initiated, promoted, and amplified or inhibited by DCs in Mtb infection is an essential step in developing anti-tuberculosis (TB) control measures, such as host-directed adjunctive therapy and anti-TB vaccines. This review summarizes the recent advances in salient DC subsets, including their phenotypic classification, cytokine profiles, functional alterations according to disease stages and environments, and consequent TB outcomes. A comprehensive overview of the role of DCs from various perspectives enables a deeper understanding of TB pathogenesis and could be useful in developing DC-based vaccines and immunotherapies.

Natural Killer Cells in SARS-CoV-2 Infection: Pathophysiology and Therapeutic Implications

Natural Killer (NK) cells are lymphocytes of the innate immunity that play a crucial role in the control of viral infections in the absence of a prior antigen sensitization. Indeed, they display rapid effector functions against target cells with the capability of direct cell killing and antibody-dependent cell-mediated cytotoxicity. Furthermore, NK cells are endowed with immune-modulatory functions innate and adaptive immune responses via the secretion of chemokines/cytokines and by undertaking synergic crosstalks with other innate immune cells, including monocyte/macrophages, dendritic cells and neutrophils. Recently, the Coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread globally. Although the specific role of NK cells in COVID-19 pathophysiology still need to be explored, mounting evidence indicates that NK cell tissue distribution and effector functions could be affected by SARS-CoV-2 infection and that a prompt NK cell response could determine a good clinical outcome in COVID-19 patients. In this review, we give a comprehensive overview of how SARS-CoV-2 infection interferes with NK cell antiviral effectiveness and their crosstalk with other innate immune cells. We also provide a detailed characterization of the specific NK cell subsets in relation to COVID-19 patient severity generated from publicly available single cell RNA sequencing datasets. Finally, we summarize the possible NK cell-based therapeutic approaches against SARS-CoV-2 infection and the ongoing clinical trials updated at the time of submission of this review. We will also discuss how a deep understanding of NK cell responses could open new possibilities for the treatment and prevention of SARS-CoV-2 infection.

High Dimensionality Reduction and Immune Phenotyping of Natural Killer and Invariant Natural Killer Cells in Latent Tuberculosis-Diabetes Comorbidity

Natural killer (NK) and invariant NKT (iNKT) cells are unique innate lymphocytes that coordinate diverse immune responses and display antimycobacterial potential. However, the role of NK and iNKT cells expressing cytokines, cytotoxic, and immune markers in latent tuberculosis (LTB), diabetes mellitus (DM), or preDM (PDM) and nonDM (NDM) comorbidities is not known. Thus, we have studied the unstimulated (UNS), Mycobacterium tuberculosis (Mtb [PPD, WCL]), and mitogen (P/I)-stimulated NK and iNKT cells expressing Type 1 (IFNγ, TNFα, and IL-2), Type 17 (IL-17A, IL-17F, and IL-22) cytokines, cytotoxic (perforin, granzyme B, and granulysin) and immune (GMCSF, PD-1, and CD69) markers in LTB comorbidities by dimensionality reduction and flow cytometry. Our results suggest that LTB DM and PDM individuals express diverse NK and iNKT cell immune clusters compared to LTB NDM individuals. In UNS condition, frequencies of NK and iNKT cells expressing markers are not significantly different. After Mtb antigen stimulation, NK cell expressing [Type 1 (IFNγ, TNFα, and IL-2), GMCSF in PPD and IFNγ in WCL), Type 17 [(IL-17A), PD-1 in PPD), (IL-17A, IL-17F, and IL-22), PD-1 in WCL], and cytotoxic (perforin, granzyme B in PPD, and WCL)] marker frequencies were significantly reduced in LTB DM and/or PDM individuals compared to LTB NDM individuals. Similarly, iNKT cells expressing [Type 1 (IFNγ, IL-2), GMCSF in PPD), TNFα, GMCSF in WCL), Type 17 (IL-17A), PD-1 in PPD, IL-17F in WCL) cytokines were increased and cytotoxic or immune (perforin, granzyme B, granulysin), CD69 in PPD, perforin and CD69 in WCL] marker frequencies were significantly diminished in LTB DM and/or PDM compared to LTB NDM individuals. Finally, NK and iNKT cell frequencies did not exhibit significant differences upon positive control antigen stimulation between the study population. Therefore, altered NK cell and iNKT cells expressing cytokines, cytotoxic, and immune markers are characteristic features in LTB PDM/DM comorbidities.

Polysaccharides from Spores of Cordyceps cicadae Protect against Cyclophosphamide-Induced Immunosuppression and Oxidative Stress in Mice

This study investigated the purification, preliminary structure and in vivo immunomodulatory activities of polysaccharides from the spores of Cordyceps cicadae (CCSP). The crude CCSP was purified by diethylaminoethyl (DEAE)-cellulose and Sephadex G-100 chromatography, affording CCSP-1, CCSP-2 and CCSP-3 with molecular weights of 1.79 × 10⁶, 5.74 × 10⁴ and 7.93 × 10³ Da, respectively. CCSP-2 consisted of mannose and glucose, while CCSP-1 and CCSP-3 are composed of three and four monosaccharides with different molar ratios, respectively. CCSP-2 exhibited its ameliorative effects in cyclophosphamide-induced immunosuppressed mice through significantly increasing spleen and thymus indices, enhancing macrophage phagocytic activity, stimulating splenocyte proliferation, improving natural killer (NK) cytotoxicity, improving bone marrow suppression, regulating the secretion of cytokines and immunoglobulins, and modulating antioxidant enzyme system. These results indicate that CCSP-2 might be exploited as a promising natural immunomodulator.

Dysconnectivity of a brain functional network was associated with blood inflammatory markers in depression

OBJECTIVE

There is increasing evidence for a subgroup of major depressive disorder (MDD) associated with heightened peripheral blood inflammatory markers. In this study, we aimed to understand the mechanistic brain-immune axis in inflammation-linked depression by investigating associations between functional connectivity (FC) of brain networks and peripheral blood immune markers in depression.

METHODS

Resting-state functional magnetic resonance imaging (fMRI) and peripheral blood inflammatory markers (C-reactive protein; CRP, interleukin-6; IL-6 and immune cells) were collected on N = 46 healthy controls (HC; CRP ≤ 3 mg/L) and N = 83 cases of depression, stratified further into low CRP cases (loCRP cases; ≤ 3 mg/L; N = 50) and high CRP cases (hiCRP cases; > 3 mg/L; N = 33). In a two-part analysis, network-based statistics (NBS) was firstly used to ascertain whole-brain FC differences in HC vs hiCRP cases. Secondly, we investigated the association between this network of interconnected brain regions and continuous measures of peripheral CRP (N = 83), IL-6 (N = 72), neutrophils and CD4⁺ T-cells (N = 36) in depression cases only.

RESULTS

Case-control NBS testing revealed a single network of abnormally attenuated FC in the high CRP depression cases compared to healthy controls. Connections within this network were mainly between brain regions located in the left insula/frontal operculum and posterior cingulate cortex, which were assigned to ventral attention and default mode canonical fMRI networks respectively. Within-group analysis across all depression cases, secondarily demonstrated that FC within the identified network significantly negatively scaled with CRP, IL-6 and neutrophils.

CONCLUSIONS

The findings suggest that inflammation is associated with disruption of functional connectivity within a brain network deemed critical for interoceptive signalling, e.g. accurate communication of peripheral bodily signals such as immune states to the brain, with implications for the pathogenesis of inflammation-linked depression.

Neutropenia and Large Granular Lymphocyte Leukemia: From Pathogenesis to Therapeutic Options

Large granular lymphocyte leukemia (LGLL) is a rare lymphoproliferative disorder characterized by the clonal expansion of cytotoxic T-LGL or NK cells. Chronic isolated neutropenia represents the clinical hallmark of the disease, being present in up to 80% of cases. New advances were made in the biological characterization of neutropenia in these patients, in particular STAT3 mutations and a discrete immunophenotype are now recognized as relevant features. Nevertheless, the etiology of LGLL-related neutropenia is not completely elucidated and several mechanisms, including humoral abnormalities, bone marrow infiltration/substitution and cell-mediated cytotoxicity might cooperate to its pathogenesis. As a consequence of the multifactorial nature of LGLL-related neutropenia, a targeted therapeutic approach for neutropenic patients has not been developed yet; moreover, specific guidelines based on prospective trials are still lacking, thus making the treatment of this disorder a complex and challenging task. Immunosuppressive therapy represents the current, although poorly effective, therapeutic strategy. The recent identification of a STAT3-mediated miR-146b down-regulation in neutropenic T-LGLL patients emphasized the pathogenetic role of STAT3 activation in neutropenia development. Accordingly, JAK/STAT3 axis inhibition and miR-146b restoration might represent tempting strategies and should be prospectively evaluated for the treatment of neutropenic LGLL patients.

Innate lymphoid cells (ILC) in SARS-CoV-2 infection

Innate Lymphoid Cells (ILCs) are a class of innate immune cells that form the first line of defense against internal or external abiotic and biotic challenges in the mammalian hosts. As they reside in both the lymphoid and non-lymphoid tissues, they are involved in clearing the pathogens through direct killing or by secretion of cytokines that modulate the adaptive immune responses. There is burgeoning evidence that these cells are important in clearing viral infections; therefore, it is critical to understand their role in the resolution or exacerbation of the disease caused by severe acute respiratory syndrome coronavirus (SARS-CoV-2). In this review, we summarize the recent findings related to ILCs in response to SARS-CoV-2 infections.

The Role of Natural Killer Cells in Autoimmune Diseases

Natural killer (NK) cells, the large granular lymphocytes differentiated from the common lymphoid progenitors, were discovered in early 1970’s. They are members of innate immunity and were initially defined by their strong cytotoxicity against virus-infected cells and by their important effector functions in anti-tumoral immune responses. Nowadays, NK cells are classified among the recently discovered innate lymphoid cell subsets and have capacity to influence both innate and adaptive immune responses. Therefore, they can be considered as innate immune cells that stands between the innate and adaptive arms of immunity. NK cells don’t express T or B cell receptors and are recognized by absence of CD3. There are two major subgroups of NK cells according to their differential expression of CD16 and CD56. While CD16⁺CD56^dim subset is best-known by their cytotoxic functions, CD16^-CD56^bright NK cell subset produces a bunch of cytokines comparable to CD4⁺ T helper cell subsets. Another subset of NK cells with production of interleukin (IL)-10 was named as NK regulatory cells, which has suppressive properties and could take part in immune-regulatory responses. Activation of NK cells is determined by a delicate balance of cell-surface receptors that have either activating or inhibitory properties. On the other hand, a variety of cytokines including IL-2, IL-12, IL-15, and IL-18 influence NK cell activity. NK-derived cytokines and their cytotoxic functions through induction of apoptosis take part in regulation of the immune responses and could contribute to the pathogenesis of many immune mediated diseases including ankylosing spondylitis, Behçet’s disease, multiple sclerosis, rheumatoid arthritis, psoriasis, systemic lupus erythematosus and type-1 diabetes. Dysregulation of NK cells in autoimmune disorders may occur through multiple mechanisms. Thanks to the rapid developments in biotechnology, progressive research in immunology enables better characterization of cells and their delicate roles in the complex network of immunity. As NK cells stand in between innate and adaptive arms of immunity and “bridge” them, their contribution in inflammation and immune regulation deserves intense investigations. Better understanding of NK-cell biology and their contribution in both exacerbation and regulation of inflammatory disorders is a requisite for possible utilization of these multi-faceted cells in novel therapeutic interventions.

Unveiling Human Non-Random Genome Editing Mechanisms Activated in Response to Chronic Environmental Changes: I. Where Might These Mechanisms Come from and What Might They Have Led To?

This article challenges the notion of the randomness of mutations in eukaryotic cells by unveiling stress-induced human non-random genome editing mechanisms. To account for the existence of such mechanisms, I have developed molecular concepts of the cell environment and cell environmental stressors and, making use of a large quantity of published data, hypothesised the origin of some crucial biological leaps along the evolutionary path of life on Earth under the pressure of natural selection, in particular, (1) virus-cell mating as a primordial form of sexual recombination and symbiosis; (2) Lamarckian CRISPR-Cas systems; (3) eukaryotic gene development; (4) antiviral activity of retrotransposon-guided mutagenic enzymes; and finally, (5) the exaptation of antiviral mutagenic mechanisms to stress-induced genome editing mechanisms directed at "hyper-transcribed" endogenous genes. Genes transcribed at their maximum rate (hyper-transcribed), yet still unable to meet new chronic environmental demands generated by "pollution", are inadequate and generate more and more intronic retrotransposon transcripts. In this scenario, RNA-guided mutagenic enzymes (e.g., Apolipoprotein B mRNA editing catalytic polypeptide-like enzymes, APOBECs), which have been shown to bind to retrotransposon RNA-repetitive sequences, would be surgically targeted by intronic retrotransposons on opened chromatin regions of the same "hyper-transcribed" genes. RNA-guided mutagenic enzymes may therefore "Lamarkianly" generate single nucleotide polymorphisms (SNP) and gene copy number variations (CNV), as well as transposon transposition and chromosomal translocations in the restricted areas of hyper-functional and inadequate genes, leaving intact the rest of the genome. CNV and SNP of hyper-transcribed genes may allow cells to surgically explore a new fitness scenario, which increases their adaptability to stressful environmental conditions. Like the mechanisms of immunoglobulin somatic hypermutation, non-random genome editing mechanisms may generate several cell mutants, and those codifying for the most environmentally adequate proteins would have a survival advantage and would therefore be Darwinianly selected. Non-random genome editing mechanisms represent tools of evolvability leading to organismal adaptation including transgenerational non-Mendelian gene transmission or to death of environmentally inadequate genomes. They are a link between environmental changes and biological novelty and plasticity, finally providing a molecular basis to reconcile gene-centred and "ecological" views of evolution.

Diminished Frequencies of Cytotoxic Marker Expressing T- and NK Cells at the Site of Mycobacterium tuberculosis Infection

Tuberculous lymphadenitis (TBL) individuals exhibit reduced frequencies of CD8⁺ T cells expressing cytotoxic markers in peripheral blood. However, the frequencies of cytotoxic marker expressing CD4⁺, CD8⁺ T cells, and NK cells at the site of infection is not known. Therefore, we measured the baseline and mycobacterial antigen specific frequencies of cytotoxic markers expressing CD4⁺, CD8⁺ T cells, and NK cells in the LN (n = 18) and whole blood (n = 10) of TBL individuals. TBL LN is associated with lower frequencies of CD4⁺ T cells expressing cytotoxic markers (Granzyme B, CD107a) compared to peripheral blood at baseline and in response to PPD, ESAT-6, and CFP-10 antigen stimulation. Similarly, lower frequencies of CD8⁺ T cells expressing cytotoxic markers (Perforin, Granzyme B, and CD107a) were also present in the TBL LN at baseline and following (except perforin) antigen stimulation. Finally, at baseline and after antigen (PPD, ESAT-6, and CFP-10) stimulation, frequencies of NK cells expressing cytotoxic markers were also significantly lower in TBL LN compared to whole blood. Hence, TBL is characterized by diminished frequencies of cytotoxic marker expressing CD4⁺, CD8⁺ T cells, and NK cells at the site of infection, which might reflect the lack of protective immune responses at the site of Mycobacterium tuberculosis infection.

Responsiveness to Influenza Vaccination Correlates with NKG2C-Expression on NK Cells

Influenza vaccination often results in a large percentage of low responders, especially in high-risk groups. As a first line of defense, natural killer (NK) cells play a crucial role in the fight against infections. However, their implication with regard to vaccine responsiveness is insufficiently assessed. Therefore, this study aimed at the validation of essential NK cell features potentially associated with differential vaccine responsiveness with a special focus on NKG2C- and/or CD57-expressing NK cells considered to harbor memory-like functions. To this end, 16 healthy volunteers were vaccinated with an adjuvanted pandemic influenza vaccine. Vaccine responders and low responders were classified according to their hemagglutination inhibition antibody titers. A majority of responders displayed enhanced frequencies of NKG2C-expressing NK cells 7- or 14-days post-vaccination as compared to low responders, whereas the expression of CD57 was not differentially modulated. The NK cell cytotoxic potential was found to be confined to CD56^dimCD16⁺ NKG2C-expressing NK cells in the responders but not in the low responders, which was further confirmed by stochastic neighbor embedding analysis. The presented study is the first of its kind that ascribes CD56^dimCD16⁺ NKG2C-expressing NK cells a crucial role in biasing adaptive immune responses upon influenza vaccination and suggests NKG2C as a potential biomarker in predicting pandemic influenza vaccine responsiveness.

Distinct Human NK Cell Phenotypes and Functional Responses to Mycobacterium tuberculosis in Adults From TB Endemic and Non-endemic Regions

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis (TB), which leads to an estimated 1. 5 million deaths worldwide each year. Although the immune correlates of protection against Mtb infection and TB disease have not been well-defined, natural killer (NK) cells are increasingly recognized as a key component of the innate immune response to Mtb and as a link between innate and adaptive immunity. In this study, we evaluated NK cell phenotypic and functional profiles in QuantiFERON-TB (QFT)⁺ and QFT⁻ adults in a TB endemic setting in Kisumu, Kenya, and compared their NK cell responses to those of Mtb-naïve healthy adult controls in the U.S. We used flow cytometry to define the phenotypic profile of NK cells and identified distinct CD56^dim NK cell phenotypes that differentiated the Kenyan and U.S. groups. Additionally, among Kenyan participants, NK cells from QFT⁺ individuals with latent Mtb infection (LTBI) were characterized by significant downregulation of the natural cytotoxicity receptor NKp46 and the inhibitory receptor TIGIT, compared with QFT⁻ individuals. Moreover, the distinct CD56^dim phenotypic profiles in Kenyan individuals correlated with dampened NK cell responses to tumor cells and diminished activation, degranulation, and cytokine production following stimulation with Mtb antigens, compared with Mtb-naïve U.S. healthy adult controls. Taken together, these data provide evidence that the phenotypic and functional profiles of NK cells are modified in TB endemic settings and will inform future studies aimed at defining NK cell-mediated immune correlates that may be protective against acquisition of Mtb infection and progression to TB disease.

Understanding the Synergy of NKp46 and Co-Activating Signals in Various NK Cell Subpopulations: Paving the Way for More Successful NK-Cell-Based Immunotherapy

The NK cell population is characterized by distinct NK cell subsets that respond differently to the various activating stimuli. For this reason, the determination of the optimal cytotoxic activation of the different NK cell subsets can be a crucial aspect to be exploited to counter cancer cells in oncologic patients. To evaluate how the triggering of different combination of activating receptors can affect the cytotoxic responses of different NK cell subsets, we developed a microbead-based degranulation assay. By using this new assay, we were able to detect CD107a⁺ degranulating NK cells even within the less cytotoxic subsets (i.e., resting CD56^bright and unlicensed CD56^dim NK cells), thus demonstrating its high sensitivity. Interestingly, signals delivered by the co-engagement of NKp46 with 2B4, but not with CD2 or DNAM-1, strongly cooperate to enhance degranulation on both licensed and unlicensed CD56^dim NK cells. Of note, 2B4 is known to bind CD48 hematopoietic antigen, therefore this observation may provide the rationale why CD56^dim subset expansion correlates with successful hematopoietic stem cell transplantation mediated by alloreactive NK cells against host T, DC and leukemic cells, while sparing host non-hematopoietic tissues and graft versus host disease. The assay further confirms that activation of LFA-1 on NK cells leads to their granule polarization, even if, in some cases, this also takes to an inhibition of NK cell degranulation, suggesting that LFA-1 engagement by ICAMs on target cells may differently affect NK cell response. Finally, we observed that NK cells undergo a time-dependent spontaneous (cytokine-independent) activation after blood withdrawal, an aspect that may strongly bias the evaluation of the resting NK cell response. Altogether our data may pave the way to develop new NK cell activation and expansion strategies that target the highly cytotoxic CD56^dim NK cells and can be feasible and useful for cancer and viral infection treatment.

Understanding the Synergy of NKp46 and Co-Activating Signals in Various NK Cell Subpopulations: Paving the Way for More Successful NK-Cell-Based Immunotherapy

The NK cell population is characterized by distinct NK cell subsets that respond differently to the various activating stimuli. For this reason, the determination of the optimal cytotoxic activation of the different NK cell subsets can be a crucial aspect to be exploited to counter cancer cells in oncologic patients. To evaluate how the triggering of different combination of activating receptors can affect the cytotoxic responses of different NK cell subsets, we developed a microbead-based degranulation assay. By using this new assay, we were able to detect CD107a⁺ degranulating NK cells even within the less cytotoxic subsets (i.e., resting CD56^bright and unlicensed CD56^dim NK cells), thus demonstrating its high sensitivity. Interestingly, signals delivered by the co-engagement of NKp46 with 2B4, but not with CD2 or DNAM-1, strongly cooperate to enhance degranulation on both licensed and unlicensed CD56^dim NK cells. Of note, 2B4 is known to bind CD48 hematopoietic antigen, therefore this observation may provide the rationale why CD56^dim subset expansion correlates with successful hematopoietic stem cell transplantation mediated by alloreactive NK cells against host T, DC and leukemic cells, while sparing host non-hematopoietic tissues and graft versus host disease. The assay further confirms that activation of LFA-1 on NK cells leads to their granule polarization, even if, in some cases, this also takes to an inhibition of NK cell degranulation, suggesting that LFA-1 engagement by ICAMs on target cells may differently affect NK cell response. Finally, we observed that NK cells undergo a time-dependent spontaneous (cytokine-independent) activation after blood withdrawal, an aspect that may strongly bias the evaluation of the resting NK cell response. Altogether our data may pave the way to develop new NK cell activation and expansion strategies that target the highly cytotoxic CD56^dim NK cells and can be feasible and useful for cancer and viral infection treatment.

Memory CD4 T cell-derived IL-2 synergizes with viral infection to exacerbate lung inflammation

Defining the most penetrating correlates of protective memory T cells is key for designing improved vaccines and T cell therapies. Here, we evaluate how interleukin (IL-2) production by memory CD4 T cells, a widely held indicator of their protective potential, impacts immune responses against murine influenza A virus (IAV). Unexpectedly, we show that IL-2-deficient memory CD4 T cells are more effective on a per cell basis at combating IAV than wild-type memory cells that produce IL-2. Improved outcomes orchestrated by IL-2-deficient cells include reduced weight loss and improved respiratory function that correlate with reduced levels of a broad array of inflammatory factors in the infected lung. Blocking CD70-CD27 signals to reduce CD4 T cell IL-2 production tempers the inflammation induced by wild-type memory CD4 T cells and improves the outcome of IAV infection in vaccinated mice. Finally, we show that IL-2 administration drives rapid and extremely potent lung inflammation involving NK cells, which can synergize with sublethal IAV infection to promote acute death. These results suggest that IL-2 production is not necessarily an indicator of protective CD4 T cells, and that the lung environment is particularly sensitive to IL-2-induced inflammation during viral infection.

When and how NK cell-induced programmed cell death benefits immunological protection against intracellular pathogen infection

NK cells are innate lymphoid cells that exert a key role in immune surveillance through the recognition and elimination of transformed cells and viral, bacterial, and protozoan pathogen-infected cells without prior sensitization. Elucidating when and how NK cell-induced intracellular microbial cell death functions in the resolution of infection and host inflammation has been an important topic of investigation. NK cell activation requires the engagement of specific activating, co-stimulatory, and inhibitory receptors which control positively and negatively their differentiation, memory, and exhaustion. NK cells secrete diverse cytokines, including IFN-γ, TNF-α/β, CD95/FasL, and TRAIL, as well as cytoplasmic cytotoxic granules containing perforin, granulysin, and granzymes A and B. Paradoxically, NK cells also kill other immune cells like macrophages, dendritic cells, and hyper-activated T cells, thus turning off self-immune reactions. Here we first provide an overview of NK cell biology, and then we describe and discuss the life–death signals that connect the microbial pathogen sensors to the inflammasomes and finally to cell death signaling pathways. We focus on caspase-mediated cell death by apoptosis and pro-inflammatory and non-caspase-mediated cell death by necroptosis, as well as inflammasome- and caspase-mediated pyroptosis.

Combination statin and chemotherapy inhibits proliferation and cytotoxicity of an aggressive natural killer cell leukemia

Background

Aggressive natural killer cell leukemia is a devastating disease, with an average patient survival time of less than 2 months following diagnosis. Due to P-glycoprotein-mediated resistance of the tumor cells most forms of chemotherapy are of limited efficacy, therefore new treatment strategies are needed. Statin drugs have recently been found to inhibit the growth of various tumor cell types.

Methods

We investigated the effects of statin drug-mediated mevalonate pathway inhibition on cell proliferation, tumor-induced cytotoxicity, cell cycle progression and ERK MAP kinase signal transduction pathway activation. Flow cytometry was used to perform the cytotoxicity and cell cycle analyses and Western blotting was used to investigate ERK MAP kinase activation. Statistical significance was assessed by Student’s t-test.

Results

Fluvastatin and atorvastatin were found to inhibit cell growth and tumor-induced cytotoxicity. These effects were reversed by the addition of mevalonate, signifying that the impact of the drugs were on the mevalonate pathway. Both drugs affected cell cycle progression by causing a significant increase in the percentage of cells in the G0/G1 phase and a reduction in the S phase and the G2/M phases of the cell cycle. Low concentrations of statin drugs were able to abrogate ERK MAP kinase pathway activation, which is typically constitutively activated in aggressive natural killer cell leukemias and important in tumor-mediated cytotoxicity. Addition of statins to chemotherapy caused enhanced inhibition of cell growth and cytotoxicity, compared to either agent alone; a combination therapy that could conceivably benefit some patients.

Conclusions

These investigations suggest that inhibiting the mevalonate pathway might provide a more effective therapy against this deadly disease when combined with chemotherapy. Given that millions of people are currently taking statin drugs to lower cholesterol levels, the risk profile for statin drugs and their side effects are well-known. Our studies suggest that it may be beneficial to explore statin-chemotherapy combination in the treatment of aggressive natural killer cell leukemias.

Vaccine therapy in hematologic malignancies

Immune-based therapy has emerged as a paradigm shift in cancer therapy with dramatic responses observed in previously incurable disease. Cancer vaccines are being developed to disrupt tumor-associated tolerance and activate and selectively expand tumor-specific lymphocytes within the native effector cell repertoire while maintaining immune-regulatory protection against autoimmunity. Although individual antigen approaches result in immune response with a suggestion of clinical effect in some settings, broader efficacy may be dependent on presentation of multiple antigens that capture clonal diversity presented in the context of functionally potent antigen-presenting cells. The use of whole cell–based strategies such as dendritic cell/tumor fusions have yielded provocative results in single-arm studies and are currently being explored in multicenter randomized trials. The posttransplant setting is a potentially promising platform for vaccination due to cytoreduction and relative depletion of inhibitory accessory cells fostering greater immune responsiveness. Integration of these efforts with other immunotherapeutic strategies and agents that target the tumor microenvironment is being studied in an effort to generate durable immunologic responses with clinically meaningful impact on disease.

Identification of GAD65 AA 114-122 reactive 'memory-like' NK cells in newly diagnosed Type 1 diabetic patients by HLA-class I pentamers

Type 1 diabetes is an autoimmune disease, in which pancreatic β cells are destroyed by autoreactive T cells in genetically predisposed individuals. Serum beta cell autoantibody specificities have represented the mainstay for classifying diabetes as autoimmune-mediated and for stratifying risk in first-degree relatives. In recent years, approaches were attempted to solve the difficult issue of detecting rare antigen-specific autoreactive T cells and their significance to etiopathogenesis such as the use of the MHC multimer technology. This tool allowed the specific detection of increased percentages of GAD65 autoreactive T cells by means of HLA A*02:01 GAD65 AA 114–122 pentamers in newly diagnosed diabetics. Here we provide evidence that GAD65 AA 114–122 pentamers can depict a GAD65 AA114-122 peptide expandable population of functionally and phenotypically skewed, preliminary characterized CD3^-CD8^dullCD56⁺ ‘memory-like’ NK cells in PBMC of newly diagnosed diabetics. Our data suggest that the NK cell subset could bind the HLA class I GAD65 AA 114–122 pentamer through ILT2 inhibitory receptor. CD107a expression revealed increased degranulation of CD3^-CD8^dullCD56⁺ NK cells in GAD65 AA 114–122 and FLU peptide expanded peripheral blood mononuclear cells of diabetics following GAD65 AA 114–122 peptide HLA A*02:01 presentation in respect to the unpulsed condition. CD107a expression was enriched in ILT2 positive NK cells. As opposite to basal conditions where similar percentages of CD3^-CD56⁺ILT2⁺ cells were detected in diabetics and controls, CD3^-CD56⁺CD107a⁺ and CD3^-CD56⁺ILT2⁺CD107a⁺ cells were significantly increased in T1D PBMC either GAD65 AA 114–122 or FLU peptides stimulated after co-culture with GAD65 AA 114–122 pulsed APCs. As control, healthy donor NK cells showed similar degranulation against both GAD65 AA 114–122 pulsed and unpulsed APCs. The pathogenetic significance of the CD3^-CD8^dullCD56⁺ ‘memory-like NK cell subset’ with increased response upon secondary challenge in diabetics remains to be elucidated.

Dengue Virus Induces NK Cell Activation through TRAIL Expression during Infection

Dengue is an acute febrile illness with a wide spectrum of signs and symptoms ranging from mild to severe forms characterized by plasma leakage that can be fatal. NK cells are one of the main effectors in early infection and may play an important role in dengue pathogenesis. We investigated NK cell involvement during dengue infection. A higher frequency of NK cell subsets and TRAIL+NK cells was found in mild DF cases when compared to that in severe cases or healthy donors. NK activation markers such as CD107a and TLR3 were upregulated in patients' cells compared to those in healthy donors. In addition, IL12 related to NK cell activation were upregulated in mild DF cases. In vitro PBMC culture models show that DENV-stimulated and IFNα-stimulated NK cells were able to express TRAIL, suggesting an indirect activation of cells, regarding TRAIL expression. Type I IFN receptor blockage on DENV-stimulated PBMCs showed TRAIL expression on NK cells is partially IFNα dependent. In addition, during PBMC stimulation, TRAIL expression on NK cells was inversely correlated with DENV-positive monocytes. Therefore, we observed DENV-induced activation of NK cell populations. A higher activation of NK cells would promote limited viral spread, resulting in decreased inflammatory response, contributing to protection against dengue severity.